The American Journal on Addictions, 24: 47–52, 2015 Copyright © American Academy of Addiction Psychiatry ISSN: 1055-0496 print / 1521-0391 online DOI: 10.1111/ajad.12171
Objective and Subjective Memory Ratings in Cannabis-Dependent Adolescents Erin A. McClure, PhD,1 Jessica B. Lydiard, BS,1 Scott D. Goddard, BS,2 Kevin M. Gray, MD1 1
Medical University of South Carolina School of Medicine, Charleston, South Carolina Texas A&M University, College Station, Texas
2
Background and Objectives: Cannabis is the most widely used illicit substance worldwide, with an estimated 160 million users. Among adolescents, rates of cannabis use are increasing, while the perception of detrimental effects of cannabis use is declining. Difficulty with memory is one of the most frequently noted cognitive deficits associated with cannabis use, but little data exist exploring how well users can identify their own memory deficits, if present. Methods: The current secondary analysis sought to characterize objective verbal and visual memory performance via a neurocognitive battery in cannabis-dependent adolescents enrolled in a pharmacotherapeutic cannabis cessation clinical trial (N ¼ 112) and compare this to a single self-reported item assessing difficulties with memory loss. Exploratory analyses also assessed dose-dependent effects of cannabis on memory performance. Results: A small portion of the study sample (10%) endorsed a “serious problem” with memory loss. Those participants reporting “no problem” or “serious problem” scored similarly on visual and verbal memory tasks on the neurocognitive battery. Exploratory analyses suggested a potential relationship between days of cannabis use, amount of cannabis used, and gender with memory performance. Conclusions and Scientific Significance: This preliminary and exploratory analysis suggests that a sub-set of cannabis users may not accurately perceive difficulties with memory. Further work should test this hypothesis with the use of a control group, comprehensive self-reports of memory problems, and adult populations that may have more years of cannabis use and more severe cognitive deficits. (Am J Addict 2015;24:47–52)
Received May 16, 2014; revised September 22, 2014; accepted October 1, 2014. Address correspondence to Dr. McClure, Clinical Neuroscience Division, Department of Psychiatry and Behavioral Sciences, Medical University of South Carolina, 125 Doughty St., Suite 190, Charleston, SC 29407. E-mail: [email protected]
INTRODUCTION Cannabis is the most widely used illicit substance worldwide, with an estimated 160 million users.1 Within the United States (US), cannabis use among adolescents is increasing, while the perception of the harmful effects of cannabis is declining.2 Cannabis use is typically initiated during adolescence or young adulthood (18.4 years old),3 and often persists into adulthood. Despite public perception of general safety, myriad problems are associated with early initiation of regular cannabis use, including higher incidence of cannabis dependence,4 neurocognitive deficits,5–7 adverse influence on relationships, employment, and mental health,8,9 and progression to the use of tobacco.10 It has been suggested that adolescents may be more vulnerable to neurocognitive deficits and alterations in brain structure and function associated with cannabis use compared to adults, due to their ongoing neurodevelopment.7,11 Further, recent work is investigating the potential link between cannabis-related brain structure abnormalities and cognitive decrements.12 Memory impairment is potentially the most frequently noted cognitive deficit associated with cannabis use. A number of studies assessing memory function in cannabis users have shown deficits associated with chronic use.13–20 Two of those studies reported on verbal learning and memory among adolescent cannabis users and found impaired memory performance among cannabis users and dose-dependent effects of cannabis on performance.18,20 While adolescent and adult data strongly suggest memory impairment in cannabis users, the perception of that impairment by the user is not well understood. Agreement between self-reported memory difficulties and objective, neurocognitive assessments has not been extensively explored in the literature. One study with aircraft pilots in a flight simulator showed that cognitive impairment was accurately perceived during acute cannabis intoxication, but impairment was not perceived 24 hour later, even in the presence of continued performance deficits.21 It may be that cannabis users are not accurately 47
identifying cognitive difficulties, thus biasing their own selfreports. The ability to accurately perceive cognitive difficulties is an important issue that warrants study, especially in adolescents, who are at a critical juncture in their educational and vocational training and advancement. The current study is an exploratory secondary analysis that assessed memory in cannabis-dependent adolescents enrolled in cannabis cessation clinical trial. Memory performance was characterized using objective and subjective measures. Visual and verbal memory was assessed through a computerized neurocognitive battery (CNS Vital Signs).22 Visual and verbal memory tasks are recognition-based, rather than recall-based, and are meant to more closely mimic memory impairments experienced during daily activities. Self-reported memory difficulties were rated via one item on The Marijuana Problem Scale (MPS).23–25 Self-reported ratings of memory loss were compared to objective performance on visual and verbal memory tasks to determine if participants could accurately recognize and report any memory difficulties. Also, dosedependent relationships between cannabis use characteristics and memory performance were explored. Based on previous research, it was expected that participants would show deficits in memory compared to previously determined age-matched control values,22 and that there would be a dose-dependent influence of cannabis use on memory performance. It was also predicted that participants would not accurately self-report their own memory difficulties. The current study did not include a control group and was not powered to test memory impairments specifically, so all analyses were exploratory in nature.
METHODS Participants and Procedures Data for this secondary analysis came from a double-blind, placebo-controlled trial of N-acetylcysteine (NAC) for cannabis cessation in treatment-seeking adolescents.26 Study participants, aged 15–21, who met criteria for cannabis dependence and had no other current clinically significant psychiatric or co-occurring substance use disorder (excluding tobacco) were enrolled (N ¼ 116 in the parent trial). Participants were excluded from the study if they were taking medications that may interfere with study medication, currently enrolled in treatment for cannabis dependence, or if they were pregnant or breastfeeding. Participants were randomized to receive active medication (NAC, 1200 mg twice daily) or matched placebo for 8 weeks. Abstinence from cannabis was the primary outcome measure in the parent trial. All memory assessments reported in this analysis were completed prior to randomization. Further details of the study can be found elsewhere.26 Measures Participants completed the self-reported MPS scale23–25 during the screening visit (prior to cannabis cessation), which 48
assesses difficulties associated with cannabis use. Specifically, the questionnaire asks participants to indicate how much of a problem a particular item has been over the past 30 days. Participants rated 19 items on an ordinal scale (0 ¼ no problem, 1 ¼ minor problem, 2 ¼ serious problem), which results in a total summed score (0–19). This questionnaire has shown excellent internal consistency (a ¼ 0.86).27 Out of 19 items, one item assesses problems with memory (ie, “memory loss”). While it is not standard practice to assess individual items from the MPS, we were specifically interested in the perception of memory difficulties, though we recognize this as a study limitation. At screening, participants also completed the CNS Vital Signs, which is a computerized neurocognitive battery of performance tests that assesses subtle changes in mental acuity, learning and memory, psychomotor speed, complex attention, impulsivity, planning and sequencing.22 Verbal and visual memory tests from this battery are adaptations of the Rey Auditory Verbal Learning Test and the Rey Visual Design Learning Test,28 which is presented with standardized instructions29 and was adapted for computer delivery.22 In the verbal task, 15 words are presented, and participants are asked to remember those words (separated by 2 second). Then, 30 words are presented with the original 15 words randomly interspersed. The participant pushes the space bar when they see a word they recognize from the previous list (immediate condition). After 20 minute, the participant is asked again to respond when they see one of the original 15 words (delay condition). In the visual task, participants are asked to remember 15 geometric shapes and the procedures are similar to those described for the verbal task. Scoring includes correct “hits” and “passes” for the immediate and delayed condition. Verbal and visual memory tasks yield scores that are summed to generate a composite memory score that captures recognition, not recall, through immediate and delayed conditions. This score can range from 60 to 120, with 100 (SD ¼ 15) being average for adolescents and young adults.22 Recency of cannabis use prior to the screening visit was captured via the Timeline Follow-Back30 adapted for cannabis use. Approximately 64% of the sample endorsed using cannabis the day prior to the screening assessment. If participants had appeared impaired at screening or reported using cannabis earlier that day, they would not have been consented at that time. Therefore, all memory measurements completed at screening were taken approximately 12–24þ hours since their last cannabis use episode (as determined by self-report). Additional questions were asked at the screening visit to assess cannabis use history (ie, years of cannabis use and number of prior quit attempts) and current use patterns (days of use in the past 30 and grams used per day). Days of use (out of the last 30) was determined via responses on the Timeline Follow-Back instrument.30 Participants were also asked to estimate the quantity of cannabis they purchase at a time and how many days that typically lasts (over the past 30 days). This provided an estimate of grams used per day.
Memory in Cannabis-Dependent Adolescents
January 2015
Statistical Analyses For the current analysis, there was insufficient data for four participants, resulting in a sample of N ¼ 112. Standard descriptive statistics were used to summarize demographic, clinical, and cannabis use characteristics for those enrolled in the parent trial, both in the aggregate and categorized by responses on the memory loss item of the MPS (0, 1, or 2). To screen for potentially confounding factors between selfreported and objective memory difficulties, Pearson chisquared tests (or Fisher’s exact tests, in cases where expected cell counts were too small) were used to compare MPS memory loss groups on categorical and grouped-continuous demographic and lifetime cannabis use measures. Similarly, a one-way ANOVA test was used to compare mean number of days of cannabis use (out of 30) and Marijuana Craving Questionnaire total score (MCQ)31 across self-reported memory loss groups. Verbal and visual memory scores from the neurocognitive battery were compared across MPS memory loss groups with the use of Kruskal–Wallis tests, owing to the non-normal residuals when performing parametric one-way ANOVA tests. Further between-group analyses were conducted with Steel– Dwass tests,32 which is the nonparametric version of Tukey’s HSD post-hoc test. In order to build a model for predicting verbal and visual memory scores, a linear model was assumed using the memory loss score from the MPS as the response variable and the full set of candidate predictors as explanatory variables, consisting of: age, gender, cigarette smoker, days of cannabis use (out of the past 30), urinary cannabinoid level, grams of cannabis used per day (past 30 days), MCQ score, modified Fagerström Tolerance Questionnaire total score (FTND),33 race (grouped: Caucasian vs. non-Caucasian), education (grouped: some college vs. no college), years of cigarette use, and years of cannabis use. A minimum Bayesian Information Criterion (BIC) stopping rule was used with a backward direction stepwise routine. Thus, the algorithm successively removed
variables from the full model and updated the model’s BIC value until no further removals could decrease the BIC any further. The remaining variables then comprised the selected model.
RESULTS Sample Characteristics Demographic and cannabis use characteristics are shown in Table 1 for all participants included in the current analysis, and separated by responses on the memory loss item of the MPS. Out of the 112 participants, 11 (10%) reported experiencing “serious” memory loss problems, while 54 (48%) reported a “minor problem” and 47 (42%) reported having “no problem” with memory loss. Generally, participants had an average (SD) age of 18.9 (1.5) years, 73% were male, and 74% were currently enrolled in school. Tests of association between the demographic and cannabis use characteristics in Table 1 and self-reported memory loss produced statistically insignificant results. The chi-squared tests found no significant association between self-reported memory loss and gender x2 (2, N ¼ 112) ¼ 5.75, p ¼ .0565; enrollment in school x2 (2, N ¼ 112) ¼ 2.65, p ¼ .266; and grams/day of cannabis (grouped) x2 (2, N ¼ 112) ¼ 2.28, p ¼ .320. Likewise, there was no significant association in the Fisher exact tests between self-reported memory loss and age (p ¼ .957), years smoking cannabis (p ¼ .868), and number of quit attempts (p ¼ .145). The means of days of cannabis use (out of 30) and MCQ total were not significantly different between the memory-loss groups, with test results of F(2, 107) ¼ 0.26, p ¼ 0.772 and F(2, 107) ¼ 1.95, p ¼ 0.147, respectively. Memory Comparisons Mean verbal and visual memory standardized scores and 95% confidence intervals (CI) derived via the CNS Vital Signs
TABLE 1. Demographic and cannabis use characteristics as a function of self-reported memory impairments
Overall (N ¼ 112), Mean SD Age Male % Enrolled in school % Years smoking cannabis # of quit attempts Days of cannabis use (out of 30) Grams/day of cannabis Marijuana craving questionnaire total (out of 84)
Marijuana problem scale Memory loss No problem Minor problem Serious problem (N ¼ 47), (N ¼ 54), (N ¼ 11), Mean SD Mean SD Mean SD
18.9 1.5 73.2 74.1 4.2 1.8 2.4 3.4 22.7 7.3
18.8 1.6 80.9 76.6 3.9 1.7 1.8 3.4 23.2 6.8
19.0 1.5 72.2 68.5 4.3 1.8 3.1 3.7 22.2 7.8
18.7 1.7 45.5 90.9 4.6 2.7 2.0 2.5 23.5 6.6
1.9 3.3 47.5 14.6
1.8 4.1 45.9 13.5
1.9 2.9 47.1 14.9
2.0 1.7 55.5 16.4
McClure et al.
January 2015
49
neurocognitive battery for all participants across memory impairment categories are listed in Table 2. Comparisons between groups revealed significant differences between the verbal and visual memory scores among the MPS groups (p ¼
Objective and Subjective Memory Ratings in Cannabis-Dependent Adolescents Erin A. McClure, PhD,1 Jessica B. Lydiard, BS,1 Scott D. Goddard, BS,2 Kevin M. Gray, MD1 1
Medical University of South Carolina School of Medicine, Charleston, South Carolina Texas A&M University, College Station, Texas
2
Background and Objectives: Cannabis is the most widely used illicit substance worldwide, with an estimated 160 million users. Among adolescents, rates of cannabis use are increasing, while the perception of detrimental effects of cannabis use is declining. Difficulty with memory is one of the most frequently noted cognitive deficits associated with cannabis use, but little data exist exploring how well users can identify their own memory deficits, if present. Methods: The current secondary analysis sought to characterize objective verbal and visual memory performance via a neurocognitive battery in cannabis-dependent adolescents enrolled in a pharmacotherapeutic cannabis cessation clinical trial (N ¼ 112) and compare this to a single self-reported item assessing difficulties with memory loss. Exploratory analyses also assessed dose-dependent effects of cannabis on memory performance. Results: A small portion of the study sample (10%) endorsed a “serious problem” with memory loss. Those participants reporting “no problem” or “serious problem” scored similarly on visual and verbal memory tasks on the neurocognitive battery. Exploratory analyses suggested a potential relationship between days of cannabis use, amount of cannabis used, and gender with memory performance. Conclusions and Scientific Significance: This preliminary and exploratory analysis suggests that a sub-set of cannabis users may not accurately perceive difficulties with memory. Further work should test this hypothesis with the use of a control group, comprehensive self-reports of memory problems, and adult populations that may have more years of cannabis use and more severe cognitive deficits. (Am J Addict 2015;24:47–52)
Received May 16, 2014; revised September 22, 2014; accepted October 1, 2014. Address correspondence to Dr. McClure, Clinical Neuroscience Division, Department of Psychiatry and Behavioral Sciences, Medical University of South Carolina, 125 Doughty St., Suite 190, Charleston, SC 29407. E-mail: [email protected]
INTRODUCTION Cannabis is the most widely used illicit substance worldwide, with an estimated 160 million users.1 Within the United States (US), cannabis use among adolescents is increasing, while the perception of the harmful effects of cannabis is declining.2 Cannabis use is typically initiated during adolescence or young adulthood (18.4 years old),3 and often persists into adulthood. Despite public perception of general safety, myriad problems are associated with early initiation of regular cannabis use, including higher incidence of cannabis dependence,4 neurocognitive deficits,5–7 adverse influence on relationships, employment, and mental health,8,9 and progression to the use of tobacco.10 It has been suggested that adolescents may be more vulnerable to neurocognitive deficits and alterations in brain structure and function associated with cannabis use compared to adults, due to their ongoing neurodevelopment.7,11 Further, recent work is investigating the potential link between cannabis-related brain structure abnormalities and cognitive decrements.12 Memory impairment is potentially the most frequently noted cognitive deficit associated with cannabis use. A number of studies assessing memory function in cannabis users have shown deficits associated with chronic use.13–20 Two of those studies reported on verbal learning and memory among adolescent cannabis users and found impaired memory performance among cannabis users and dose-dependent effects of cannabis on performance.18,20 While adolescent and adult data strongly suggest memory impairment in cannabis users, the perception of that impairment by the user is not well understood. Agreement between self-reported memory difficulties and objective, neurocognitive assessments has not been extensively explored in the literature. One study with aircraft pilots in a flight simulator showed that cognitive impairment was accurately perceived during acute cannabis intoxication, but impairment was not perceived 24 hour later, even in the presence of continued performance deficits.21 It may be that cannabis users are not accurately 47
identifying cognitive difficulties, thus biasing their own selfreports. The ability to accurately perceive cognitive difficulties is an important issue that warrants study, especially in adolescents, who are at a critical juncture in their educational and vocational training and advancement. The current study is an exploratory secondary analysis that assessed memory in cannabis-dependent adolescents enrolled in cannabis cessation clinical trial. Memory performance was characterized using objective and subjective measures. Visual and verbal memory was assessed through a computerized neurocognitive battery (CNS Vital Signs).22 Visual and verbal memory tasks are recognition-based, rather than recall-based, and are meant to more closely mimic memory impairments experienced during daily activities. Self-reported memory difficulties were rated via one item on The Marijuana Problem Scale (MPS).23–25 Self-reported ratings of memory loss were compared to objective performance on visual and verbal memory tasks to determine if participants could accurately recognize and report any memory difficulties. Also, dosedependent relationships between cannabis use characteristics and memory performance were explored. Based on previous research, it was expected that participants would show deficits in memory compared to previously determined age-matched control values,22 and that there would be a dose-dependent influence of cannabis use on memory performance. It was also predicted that participants would not accurately self-report their own memory difficulties. The current study did not include a control group and was not powered to test memory impairments specifically, so all analyses were exploratory in nature.
METHODS Participants and Procedures Data for this secondary analysis came from a double-blind, placebo-controlled trial of N-acetylcysteine (NAC) for cannabis cessation in treatment-seeking adolescents.26 Study participants, aged 15–21, who met criteria for cannabis dependence and had no other current clinically significant psychiatric or co-occurring substance use disorder (excluding tobacco) were enrolled (N ¼ 116 in the parent trial). Participants were excluded from the study if they were taking medications that may interfere with study medication, currently enrolled in treatment for cannabis dependence, or if they were pregnant or breastfeeding. Participants were randomized to receive active medication (NAC, 1200 mg twice daily) or matched placebo for 8 weeks. Abstinence from cannabis was the primary outcome measure in the parent trial. All memory assessments reported in this analysis were completed prior to randomization. Further details of the study can be found elsewhere.26 Measures Participants completed the self-reported MPS scale23–25 during the screening visit (prior to cannabis cessation), which 48
assesses difficulties associated with cannabis use. Specifically, the questionnaire asks participants to indicate how much of a problem a particular item has been over the past 30 days. Participants rated 19 items on an ordinal scale (0 ¼ no problem, 1 ¼ minor problem, 2 ¼ serious problem), which results in a total summed score (0–19). This questionnaire has shown excellent internal consistency (a ¼ 0.86).27 Out of 19 items, one item assesses problems with memory (ie, “memory loss”). While it is not standard practice to assess individual items from the MPS, we were specifically interested in the perception of memory difficulties, though we recognize this as a study limitation. At screening, participants also completed the CNS Vital Signs, which is a computerized neurocognitive battery of performance tests that assesses subtle changes in mental acuity, learning and memory, psychomotor speed, complex attention, impulsivity, planning and sequencing.22 Verbal and visual memory tests from this battery are adaptations of the Rey Auditory Verbal Learning Test and the Rey Visual Design Learning Test,28 which is presented with standardized instructions29 and was adapted for computer delivery.22 In the verbal task, 15 words are presented, and participants are asked to remember those words (separated by 2 second). Then, 30 words are presented with the original 15 words randomly interspersed. The participant pushes the space bar when they see a word they recognize from the previous list (immediate condition). After 20 minute, the participant is asked again to respond when they see one of the original 15 words (delay condition). In the visual task, participants are asked to remember 15 geometric shapes and the procedures are similar to those described for the verbal task. Scoring includes correct “hits” and “passes” for the immediate and delayed condition. Verbal and visual memory tasks yield scores that are summed to generate a composite memory score that captures recognition, not recall, through immediate and delayed conditions. This score can range from 60 to 120, with 100 (SD ¼ 15) being average for adolescents and young adults.22 Recency of cannabis use prior to the screening visit was captured via the Timeline Follow-Back30 adapted for cannabis use. Approximately 64% of the sample endorsed using cannabis the day prior to the screening assessment. If participants had appeared impaired at screening or reported using cannabis earlier that day, they would not have been consented at that time. Therefore, all memory measurements completed at screening were taken approximately 12–24þ hours since their last cannabis use episode (as determined by self-report). Additional questions were asked at the screening visit to assess cannabis use history (ie, years of cannabis use and number of prior quit attempts) and current use patterns (days of use in the past 30 and grams used per day). Days of use (out of the last 30) was determined via responses on the Timeline Follow-Back instrument.30 Participants were also asked to estimate the quantity of cannabis they purchase at a time and how many days that typically lasts (over the past 30 days). This provided an estimate of grams used per day.
Memory in Cannabis-Dependent Adolescents
January 2015
Statistical Analyses For the current analysis, there was insufficient data for four participants, resulting in a sample of N ¼ 112. Standard descriptive statistics were used to summarize demographic, clinical, and cannabis use characteristics for those enrolled in the parent trial, both in the aggregate and categorized by responses on the memory loss item of the MPS (0, 1, or 2). To screen for potentially confounding factors between selfreported and objective memory difficulties, Pearson chisquared tests (or Fisher’s exact tests, in cases where expected cell counts were too small) were used to compare MPS memory loss groups on categorical and grouped-continuous demographic and lifetime cannabis use measures. Similarly, a one-way ANOVA test was used to compare mean number of days of cannabis use (out of 30) and Marijuana Craving Questionnaire total score (MCQ)31 across self-reported memory loss groups. Verbal and visual memory scores from the neurocognitive battery were compared across MPS memory loss groups with the use of Kruskal–Wallis tests, owing to the non-normal residuals when performing parametric one-way ANOVA tests. Further between-group analyses were conducted with Steel– Dwass tests,32 which is the nonparametric version of Tukey’s HSD post-hoc test. In order to build a model for predicting verbal and visual memory scores, a linear model was assumed using the memory loss score from the MPS as the response variable and the full set of candidate predictors as explanatory variables, consisting of: age, gender, cigarette smoker, days of cannabis use (out of the past 30), urinary cannabinoid level, grams of cannabis used per day (past 30 days), MCQ score, modified Fagerström Tolerance Questionnaire total score (FTND),33 race (grouped: Caucasian vs. non-Caucasian), education (grouped: some college vs. no college), years of cigarette use, and years of cannabis use. A minimum Bayesian Information Criterion (BIC) stopping rule was used with a backward direction stepwise routine. Thus, the algorithm successively removed
variables from the full model and updated the model’s BIC value until no further removals could decrease the BIC any further. The remaining variables then comprised the selected model.
RESULTS Sample Characteristics Demographic and cannabis use characteristics are shown in Table 1 for all participants included in the current analysis, and separated by responses on the memory loss item of the MPS. Out of the 112 participants, 11 (10%) reported experiencing “serious” memory loss problems, while 54 (48%) reported a “minor problem” and 47 (42%) reported having “no problem” with memory loss. Generally, participants had an average (SD) age of 18.9 (1.5) years, 73% were male, and 74% were currently enrolled in school. Tests of association between the demographic and cannabis use characteristics in Table 1 and self-reported memory loss produced statistically insignificant results. The chi-squared tests found no significant association between self-reported memory loss and gender x2 (2, N ¼ 112) ¼ 5.75, p ¼ .0565; enrollment in school x2 (2, N ¼ 112) ¼ 2.65, p ¼ .266; and grams/day of cannabis (grouped) x2 (2, N ¼ 112) ¼ 2.28, p ¼ .320. Likewise, there was no significant association in the Fisher exact tests between self-reported memory loss and age (p ¼ .957), years smoking cannabis (p ¼ .868), and number of quit attempts (p ¼ .145). The means of days of cannabis use (out of 30) and MCQ total were not significantly different between the memory-loss groups, with test results of F(2, 107) ¼ 0.26, p ¼ 0.772 and F(2, 107) ¼ 1.95, p ¼ 0.147, respectively. Memory Comparisons Mean verbal and visual memory standardized scores and 95% confidence intervals (CI) derived via the CNS Vital Signs
TABLE 1. Demographic and cannabis use characteristics as a function of self-reported memory impairments
Overall (N ¼ 112), Mean SD Age Male % Enrolled in school % Years smoking cannabis # of quit attempts Days of cannabis use (out of 30) Grams/day of cannabis Marijuana craving questionnaire total (out of 84)
Marijuana problem scale Memory loss No problem Minor problem Serious problem (N ¼ 47), (N ¼ 54), (N ¼ 11), Mean SD Mean SD Mean SD
18.9 1.5 73.2 74.1 4.2 1.8 2.4 3.4 22.7 7.3
18.8 1.6 80.9 76.6 3.9 1.7 1.8 3.4 23.2 6.8
19.0 1.5 72.2 68.5 4.3 1.8 3.1 3.7 22.2 7.8
18.7 1.7 45.5 90.9 4.6 2.7 2.0 2.5 23.5 6.6
1.9 3.3 47.5 14.6
1.8 4.1 45.9 13.5
1.9 2.9 47.1 14.9
2.0 1.7 55.5 16.4
McClure et al.
January 2015
49
neurocognitive battery for all participants across memory impairment categories are listed in Table 2. Comparisons between groups revealed significant differences between the verbal and visual memory scores among the MPS groups (p ¼
